WASHINGTON (Reuters) - Prosthetics maker Otto Bock HealthCare GMBH’s (IPO-OBH.F) purchase of rival FIH Group Holdings should be undone because it hurt competition in the business of making prosthetic knees with microprocessors, the U.S. antitrust regulator said in a complaint on Wednesday.

The U.S. Federal Trade Commission said it has filed a complaint challenging the deal, which closed in September.

Otto Bock did not immediately respond to a request for comment when contacted outside of European business hours.

Prosthetic knees with microprocessors are better at adjusting to different terrain and styles of walking. They reduce the risk of falls.